40 CFR § 63.3 - Units and abbreviations.

---
identifier: "/us/cfr/t40/s63.3"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 63.3 - Units and abbreviations."
title_number: 40
title_name: "Protection of Environment"
section_number: "63.3"
section_name: "Units and abbreviations."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "63"
part_name: "NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE CATEGORIES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401"
regulatory_source: "57 FR 61992, Dec. 29, 1992, unless otherwise noted."
cfr_part: "63"
---


# 63.3 Units and abbreviations.

Used in this part are abbreviations and symbols of units of measure. These are defined as follows:

(a) *System International (SI) units of measure:*

A = ampere

g = gram

Hz = hertz

J = joule

°K = degree Kelvin

kg = kilogram

l = liter

m = meter

m
<sup>3</sup> = cubic meter

mg = milligram = 10<sub>−3</sub> gram

ml = milliliter = 10<sub>−3</sub> liter

mm = millimeter = 10<sub>−3</sub> meter

Mg = megagram = 10
<sup>6</sup> gram = metric ton

MJ = megajoule

mol = mole

N = newton

ng = nanogram = 10<sub>−9</sub> gram

nm = nanometer = 10<sub>−9</sub> meter

Pa = pascal

s = second

V = volt

W = watt

Ω = ohm

µg = microgram = 10<sub>−6</sub> gram

µl = microliter = 10<sub>−6</sub> liter

(b) *Other units of measure:*

Btu = British thermal unit

°C = degree Celsius (centigrade)

cal = calorie

cfm = cubic feet per minute

cc = cubic centimeter

cu ft = cubic feet

d = day

dcf = dry cubic feet

dcm = dry cubic meter

dscf = dry cubic feet at standard conditions

dscm = dry cubic meter at standard conditions

eq = equivalent

°F degree Fahrenheit

ft = feet

ft
<sup>2</sup> = square feet

ft
<sup>3</sup> = cubic feet

gal = gallon

gr = grain

g-eq = gram equivalent

g-mole = gram mole

hr = hour

in. = inch

in. H<sub>2</sub> O = inches of water

K = 1,000

kcal = kilocalorie

lb = pound

lpm = liter per minute

meq = milliequivalent

min = minute

MW = molecular weight

oz = ounces

ppb = parts per billion

ppbw = parts per billion by weight

ppbv = parts per billion by volume

ppm = parts per million

ppmw = parts per million by weight

ppmv = parts per million by volume

psia = pounds per square inch absolute

psig = pounds per square inch gage

°R = degree Rankine

scf = cubic feet at standard conditions

scfh = cubic feet at standard conditions per hour

scm = cubic meter at standard conditions

scmm = cubic meter at standard conditions per minute

sec = second

sq ft = square feet

std = at standard conditions

v/v = volume per volume

yd
<sup>2</sup> = square yards

yr = year

(c) *Miscellaneous:*

act = actual

avg = average

I.D. = inside diameter

M = molar

N = normal

O.D. = outside diameter

% = percent

[59 FR 12430, Mar. 16, 1994, as amended at 67 FR 16598, Apr. 5, 2002]